This invention relates to harvesting blood vessels for coronary artery bypass grafting (hereinafter xe2x80x9cCABGxe2x80x9d), and more particularly to a device for facilitating harvesting internal mammary arteries for anastomosis to coronary arteries using minimally invasive procedures. Minimally invasive procedures are employed to minimize trauma to the patient in order to promote rapid healing and reduce the amount of pain during recovery. This invention relates particularly to a blood vessel harvesting apparatus that can be used for forming a small anatomic working space alongside an elongate vessel, particularly a blood vessel, and more particularly a small blood vessel such as an internal mammary artery (hereinafter xe2x80x9cIMAxe2x80x9d). The invention relates specifically to an assembly having a cannula and an assembled balloon.
Diseases of the cardiovascular system affect millions of people each year and are a leading cause of death in the United States and throughout the world. The cost to society from such diseases is enormous both in terms of lives lost and the cost of treating cardiac disease patients through surgery. A particularly prevalent form of cardiovascular disease is a reduction in the blood supply to the heart caused by atherosclerosis or other conditions that create a restriction in blood flow in the arteries supplying blood to the heart.
Numerous surgical procedures have been developed to restore blood flow to the heart. For example, blockages can be treated with atherectomy or angioplasty, often followed by stent placement. But, when these methods of treatment cannot be used or have failed to clear the blocked artery, coronary bypass surgery may be indicated.
In the CABG procedure, the surgeon removes a portion of an artery or vein from another part of the body to use as a graft and installs the graft to bypass the obstruction. Alternatively, the surgeon dissects a healthy artery adjacent to the diseased artery, detaches one end of the healthy artery and connects that end to the coronary artery past the obstruction while leaving the other end attached to the natural arterial supply. Either of these two methods can restore normal blood flow to the heart.
The CABG procedure thus requires that one or more connections be established that bypass blockage in a diseased artery to restore an adequate blood flow. Typically, one end of a graft is sewn to the aorta, while the other end of the graft is sewn to a coronary artery, such as the left anterior descending artery (LAD), which provides blood flow to the left side of the heart. This procedure is known as a xe2x80x9cfree bypass graft.xe2x80x9d Alternatively, the IMA pedicle may be dissected free of the chest wall, while still attached to its natural arterial supply, and its distal end attached to the blocked artery distal of the obstruction. This procedure is known as an xe2x80x9cin situ bypass graft.xe2x80x9d
In an in situ bypass graft, the IMA must be dissected free until there is sufficient length and slack in the IMA to ensure that the graft is not under tension and that it does not kink after it is repositioned. The IMAs, left and right, extend from the subclavian arteries in the neck to the diaphragm and run along the backside of the rib cage adjacent the sternum. They also contain side branches that require ligation to ensure that blood flow through the graft supplies the coronary artery, rather than being shunted off to other regions via various open branches.
Traditional methods for harvesting elongate vessels such as the IMAs involve the use of blunt probes that are pushed through body tissue to accomplish the dissection. (See Chin, U.S. Pat. No. 5,797,946, incorporated herein by reference). But, the force exerted during use of mechanical probes may lead to blood vessel trauma and branch avulsion.
Everting balloons, on the other hand, are more gentle and may be used to dissect along a vessel. But, it is difficult for the everting balloons presently available to follow vessels such as the IMAs. This is caused by the greater fixation that exists between these vessels and the tissue that surrounds them and to the characteristics of existing everting balloon dissectors. For example, a traditional everting balloon placed adjacent the saphenous vein in the leg, may squirt off in either direction upon inflation rather than track along the vein. This is due to the anatomical structures and to the fixation between the saphenous vein and the tissues that surround the vein.
Another problem associated with balloon dissectors adjacent a blood vessel is that after an initial dissection, a second dissection is more difficult. After connective tissue separating two layers of tissue has been ruptured due to an initial dissection, the healing process that ensues may involve formation of scar tissue. The scar tissue replacing the normal connective tissue is more difficult to dissect. The everting balloons presently available have difficulty tracking along a blood vessel through such scar tissue.
A need exists for new devices with adequate directional control to dissect small elongated cavities in tissue planes, particularly along the course of blood vessels, and more particularly, along the course of smaller blood vessels such as IMAs. A need also exists for new devices to dissect elongated cavities in tissue planes that have been dissected previously.
The present invention provides a cannula assembly for dissecting an elongated cavity in tissue planes, particularly along the course of a vessel, and more particularly along the course of a smaller blood vessel such as an IMA. The assembly includes an elongate tubular member comprising a hollow tube having a wall, proximal and distal ends and a lumen extending therethrough. In one embodiment, the hollow tube has a flattened or oval shaped distal end that is bent to facilitate insertion in between the ribs. Alternatively, the hollow tube can have an ogee offset at its distal end.
The dissection device also has means for connecting the hollow tube to an inflation source in order to inflate an elongate tubular balloon in fluid communication with the hollow tube. The means for connecting the hollow tube to an inflation source include an opening in the proximal end of the hollow tube or an opening in the wall of the hollow tube. Fluid, gas, or a liquid such as water or saline, can therefore be delivered from a syringe, a hand bulb pump, a piston pump, or the like to the interior of the elongate tubular balloon.
An elongate tubular balloon having an open proximal end and a closed distal end is coupled to the hollow tube and may be inverted and stored inside the hollow tube. The open proximal end of the elongate tubular balloon is coupled in a fluid-tight manner to the hollow tube. In one embodiment, the proximal end of the elongate tubular balloon is sealed around the outer wall of the hollow tube at its distal end. However, the open proximal end of the elongate tubular balloon may also be sealed to the lumen of the hollow tube or around the outer wall of the hollow tube at its proximal end.
The distal portion of the deflated elongate tubular balloon can be inverted toward the proximal portion and stored inside the hollow tube or in a reservoir formed in the balloon itself. Thus, in its deflated state, the distal end of the elongate tubular balloon may be stored proximal of its proximal end. Additional inward folds may be used to further shorten the length of the deflated elongate tubular balloon.
During inflation, this inverted embodiment of the elongate tubular balloon everts and advances beyond the distal end of the hollow tube until it is completely inflated. The fully inflated elongate tubular balloon can be as long as or longer than the hollow tube.
The dissection device also comprises a means for deflating the elongate tubular balloon, such as a vent or a deflation valve on the hollow tube. The elongate tubular balloon may be inflated and deflated multiple times during a single use.
The dissection device may also include means for retracting and re-inverting the elongate tubular balloon so that it can be re-inflated for multiple use during a surgical procedure. Means for retracting and re-inverting may include push rods, guide rods, or retraction lines comprising wire or string attached to the distal portion of the balloon.
It can be appreciated that the elongate tubular balloon of the present invention can have multiple chambers running substantially the entire length of the balloon. Multiple chambers serve to add lateral rigidity to the elongate balloon as it inflates while minimizing the cross-section of the dissected space created. The elongate tubular balloon can have one chamber, more preferably five chambers, more preferably four chambers, more preferably three chambers and most preferably two chambers. However, other embodiments having a greater number of chambers are also contemplated.
It has been found preferable to utilize a nonelastomeric balloon so that it is possible to control the shape of the dissected region. The fully inflated balloon can have an axial length of 5 to 30 inches, a width of 0.50 to 2.5 inches, and a height of 0.10 to 1.0 inches. The balloon can be formed as described in Kieturakis et al., U.S. Pat. No. 5,496,345, the entirety of which is incorporated herein by reference.
In one embodiment, the elongate tubular balloon has two cylindrical chambers running substantially the entire length of the balloon. The two chambers are in fluid communication with each other. A weld running substantially the entire length of the balloon may accomplish this double chambered configuration. The double chambered configuration decreases the likelihood that the everting balloon will track laterally off course as it everts, and it also eases insertion and tracking along the narrow space available between the sternum and the IMA and other surrounding tissue.
The double chambered configuration flattens the elongate tubular balloon, thus making it easier for the elongate tubular balloon to settle into a natural tissue plane. With a wider profile and a decreased height, the elongate tubular balloon is more likely to track along a natural tissue plane without changing its course laterally in an undesirable direction. If desired, the elongate tubular balloon may be curved to follow a desired path.
Moreover, with a left chamber and a right chamber, the lateral rigidity of the elongate tubular balloon increases for any given cross-section. This is because the width of an elongate tubular balloon that has been flattened by adding a weld along its length is greater than the height of the balloon. Thus, the moment of inertia will be higher in the plane defined by the width of the elongate tubular balloon than in the plane defined by the height of the elongate tubular balloon. Therefore, the double chambered configuration of the present invention will be less likely to bend transversely toward the left or right chambers as it everts along a natural tissue plane. Furthermore, it is not likely to bend in an upward or downward direction since it will be prevented from doing so by both the natural tissue layer above it and the natural tissue layer below it. Therefore, the double chambered everting elongate tubular balloon of the present invention is better suited for controlled dissection along smaller arteries such as the IMAs, which are tightly adhered to the tissue that surrounds them.
The flattened profile of the double chambered balloon is also desirable because the distance from the sternum to either the right or left IMA is about half an inch. This distance does not change substantially at any point along the length of either of the IMAs. Therefore, a flatter profile balloon is preferred to track along the narrow space available between the sternum and the IMA. Furthermore, a flat profile balloon is preferred over a thin and round balloon for dissecting along arteries such as IMAs for the reasons stated above with respect to lateral rigidity.
In a cannula assembly comprising a double chambered elongate tubular balloon, the balloon can be inverted by pulling or pushing the distal end of the balloon proximally through one of the chambers. Thus, in a deflated state, one of the chambers of the double chambered elongate tubular balloon is stored inside the other inverted chamber. Substantially the entire length of the deflated elongate tubular balloon can be stored inside the hollow tube. Upon inflation, the distal end of the balloon begins to evert outwardly and propagate in a distal direction until the balloon has completely everted and extends outside of the hollow tube. The propagation of the everting balloon can be facilitated by coating the internal surface, the external surface, or both surfaces of the balloon with a lubricant.
Alternatively, the two cylindrical chambers of the elongate tubular balloon can be formed by shifting the line of the weld to one side, thus resulting in one chamber having a larger cross-section than the other. This configuration may ease inversion and eversion, because there is a larger inverting chamber into which the smaller chamber follows during inversion and from which it exits during eversion.
In other embodiments of the present invention, the elongate tubular balloon has three, four or five chambers running substantially the entire length of the balloon. The chambers can be in fluid communication with each other or entirely separated and separately inflated. Welds running substantially the entire length of the balloon accomplish these configurations. Like the double-chambered elongate tubular balloon, the three, four and five-chambered configurations decrease the likelihood that the everting balloons will track off course as they evert, and they also ease insertion and tracking along the narrow space available between the sternum and the IMA. However, elongate tubular balloons having more than five chambers are also contemplated.
In another embodiment the dissection device is designed for use with an endoscope or laparoscope. The proximal end of the hollow tube of the dissection device is adapted to receive, and if necessary, seal around the scope. The scope can be inserted through the proximal end of the hollow tube and advanced toward the distal end of the hollow tube either while the elongate tubular balloon is being inflated or after the elongate tubular balloon is completely inflated and is in its everted position. In the case of a multi-chambered elongate tubular balloon, the scope can be, advanced through any one of the chambers. Alternatively, the scope can be independently inserted through the incision and advanced alongside the elongate tubular balloon as the balloon everts and dissects along the IMA or after the balloon is fully inflated.
Another embodiment of the dissection device comprises a guide rod, the distal end of which is inserted through the proximal end of the hollow tube and attached to the distal end of the elongate tubular balloon. Thus, eversion of the elongate tubular balloon and dissection along the IMA can be done either by advancing the guide rod along the IMA while inflating the balloon at the same time, or by advancing the guide rod along the IMA to the desired point and thereafter inflating the elongate tubular balloon. The guide rod can also be used to retract the elongate tubular balloon back into the hollow tube, at the same time re-inverting the elongate tubular balloon for withdrawal or subsequent use. A guide rod can be used either in a single chambered elongate tubular balloon or a multi-chambered elongate tubular balloon and may be attached to the distal end of the balloon, or may be loose.
Another embodiment of the dissection device comprises a guide rod, as above described, which is attached to a shorter balloon having a larger cross-section upon inflation. The hollow tube of this embodiment is longer than in the other embodiments earlier described to compensate for the decreased length of the balloon. Dissection is accomplished by 1) advancing the guide rod a short distance along, for example the IMA, for blunt dissection, probing between the IMA and the adjacent tissue in the plane initiated by this method of blunt dissection, 2) inflating the balloon to further dissect the IMA from the tissue adjacent to it, 3) deflating the balloon and 4) repeating steps one through three along the length of the IMA desired for the coronary artery bypass graft.
Another embodiment of the invention comprises a double-chambered elongate tubular balloon having a laterally extending thumb-shaped reservoir. A housing having a tubular balloon sleeve extending therefrom terminates the balloon and may receive a laparoscope. In its deflated and undeployed state, one chamber of the balloon is stored within the other chamber as previously described, and the distal portion of the balloon is stored inside the thumb-shaped reservoir.
Additional features of the invention will appear from the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings.